1. Field of the Invention
This invention relates to a method and an apparatus for treating water containing organic sulfur compounds, and more particularly, a method for biologically decomposing water such as wastewater containing organic sulfur compounds such as dimetyl sulfoxido (DMSO), etc., while suppressing offensive odor, and an apparatus for carrying out such decomposition.
2. Description of the Prior Art
Referring to FIG. 4, a conventional apparatus of this type comprises a storage tank 1a storing raw water as water to be treated, a pH adjustment tank 2a for adjusting the pH value of the water fed from the storage tank 1a, a biological treatment tank 8a for biologically treating the water whose pH value is adjusted by the pH adjustment tank 2a, and a precipitation tank 15a to which the water treated at the biological treatment tank 8a is supplied.
The pH adjustment tank 2a includes a pH measuring instrument 3a for measuring the pH value in the pH adjustment tank 2a, an alkali pump 4a as an alkali supplying means for supplying alkaline liquid into the pH adjustment tank 2a, and a controller 6a for controlling the volume of the alkaline liquid supplied by the alkali pump 4a in accordance with the pH value measured by the pH measuring instrument 3a.
In the apparatus of this arrangement, after the water is temporarily stored in the storage tank 1a, the alkaline liquid is added to the pH adjustment tank 2a to a predetermined pH value, and then, is supplied to the biological treatment tank 8a.
The water is subjected to oxidation decomposition by microorganisms, as the water flows down to an effluent end side in the biological treatment tank 8a. Oxygen required for microorganisms is successively fed by an aerator installed in the biological treatment tank 8a.
The water treated in the biological treatment tank 8a is separated into sludge containing microorganisms and the treated water in the precipitation tank 15a, and the sludge settled in the precipitation tank 15a is returned to the biological treatment tank 8a or withdrawn outside the system.
However, in case of treating the water with such conventional treatment apparatus, following problems are caused.
(1) At an inlet of the biological treatment tank, the concentration of the organic sulfur compounds increases.
Of organic sulfur compounds, DMSO, etc. adversely affect to organisms, when the substrate concentration thereof exceeds a certain level, lowers the decomposition speed and removal rate of organic sulfur compounds, halts progress of the decomposition, and generates methyl sulfide, methylmercaptan and the like which are component of offensive odor.
(2) Organic sulfur compounds gradually decompose as they flow down in the biological treatment tank, and sulfuric ions are proportionally formed. Accordingly, the concentration of sulfuric ions gradually becomes high towards an outlet of the biological treatment tank.
When organic sulfur compounds of a high concentration are biologically decomposed, since the concentration of sulfuric ions generated is relatively high at the outlet, it is difficult to add, at an inlet of the biological treatment tank, alkali which will become necessary at the outlet of the biological treatment tank for neutralization of sulfuric ions, while properly maintaining the pH value in the overall biological treatment tank.
The decomposition speed and removal rate of organic sulfur compounds are lowered due to the lowering of the pH value. As a result, progress of decomposition is halted, and offensive odor component, such as methyl sulfide and methylmercaptan are generated.
(3) During organic sulfur compounds are biologically treated, not only carbon and hydrogen, but also sulfur must be oxidized. Subsequently, the required oxygen volume increases, possibly resulting in shortage of dissolved oxygen in the biological treatment tank.
Once reducing atmosphere is formed by the shortage of dissolved oxygen, methyl sulfide, methylmercaptan and the like of offensive odor component are generated.
(4) When the microorganisms are overloaded with organic sulfur compounds, diffusion and penetration of oxygen to activated sludge floc, a biological membrane and the like do not take place satisfactorily, resulting in the generation of odor components, such as methyl sulfide and methylmercaptan, in the similar manner as Item (3).